[linux.git] / drivers / md / dm-zero.c

/*
 * Copyright (C) 2003 Jana Saout <[email protected]>
 *
 * This file is released under the GPL.
 */

#include <linux/device-mapper.h>

#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>

#define DM_MSG_PREFIX "zero"

/*
 * Construct a dummy mapping that only returns zeros
 */
static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
	if (argc != 0) {
		ti->error = "No arguments required";
		return -EINVAL;
	}

	/*
	 * Silently drop discards, avoiding -EOPNOTSUPP.
	 */
	ti->num_discard_bios = 1;

	return 0;
}

/*
 * Return zeros only on reads
 */
static int zero_map(struct dm_target *ti, struct bio *bio)
{
	switch(bio_rw(bio)) {
	case READ:
		zero_fill_bio(bio);
		break;
	case READA:
		/* readahead of null bytes only wastes buffer cache */
		return -EIO;
	case WRITE:
		/* writes get silently dropped */
		break;
	}

	bio_endio(bio);

	/* accepted bio, don't make new request */
	return DM_MAPIO_SUBMITTED;
}

static struct target_type zero_target = {
	.name   = "zero",
	.version = {1, 1, 0},
	.module = THIS_MODULE,
	.ctr    = zero_ctr,
	.map    = zero_map,
};

static int __init dm_zero_init(void)
{
	int r = dm_register_target(&zero_target);

	if (r < 0)
		DMERR("register failed %d", r);

	return r;
}

static void __exit dm_zero_exit(void)
{
	dm_unregister_target(&zero_target);
}

module_init(dm_zero_init)
module_exit(dm_zero_exit)

MODULE_AUTHOR("Jana Saout <[email protected]>");
MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
MODULE_LICENSE("GPL");
Commit	Line	Data
1da177e4	1	/*
bf14299f	2	* Copyright (C) 2003 Jana Saout <[email protected]>
1da177e4 LT	3	*
	4	* This file is released under the GPL.
	5	*/
	6
586e80e6	7	#include <linux/device-mapper.h>
1da177e4 LT	8
	9	#include <linux/module.h>
	10	#include <linux/init.h>
	11	#include <linux/bio.h>
	12
72d94861 AK	13	#define DM_MSG_PREFIX "zero"
72d94861 AK	14
1da177e4 LT	15	/*
	16	* Construct a dummy mapping that only returns zeros
	17	*/
	18	static int zero_ctr(struct dm_target ti, unsigned int argc, char *argv)
	19	{
	20	if (argc != 0) {
72d94861	21	ti->error = "No arguments required";
1da177e4 LT	22	return -EINVAL;
	23	}
	24
f8facb61 MS	25	/*
	26	* Silently drop discards, avoiding -EOPNOTSUPP.
	27	*/
55a62eef	28	ti->num_discard_bios = 1;
f8facb61	29
1da177e4 LT	30	return 0;
	31	}
	32
	33	/*
	34	* Return zeros only on reads
	35	*/
7de3ee57	36	static int zero_map(struct dm_target ti, struct bio bio)
1da177e4 LT	37	{
	38	switch(bio_rw(bio)) {
	39	case READ:
	40	zero_fill_bio(bio);
	41	break;
	42	case READA:
	43	/* readahead of null bytes only wastes buffer cache */
	44	return -EIO;
	45	case WRITE:
	46	/* writes get silently dropped */
	47	break;
	48	}
	49
4246a0b6	50	bio_endio(bio);
1da177e4 LT	51
1da177e4 LT	52	/* accepted bio, don't make new request */
d2a7ad29	53	return DM_MAPIO_SUBMITTED;
1da177e4 LT	54	}
	55
	56	static struct target_type zero_target = {
	57	.name = "zero",
7de3ee57	58	.version = {1, 1, 0},
1da177e4 LT	59	.module = THIS_MODULE,
	60	.ctr = zero_ctr,
	61	.map = zero_map,
	62	};
	63
5e198d94	64	static int __init dm_zero_init(void)
1da177e4 LT	65	{
	66	int r = dm_register_target(&zero_target);
	67
	68	if (r < 0)
72d94861	69	DMERR("register failed %d", r);
1da177e4 LT	70
	71	return r;
	72	}
	73
5e198d94	74	static void __exit dm_zero_exit(void)
1da177e4	75	{
10d3bd09	76	dm_unregister_target(&zero_target);
1da177e4 LT	77	}
	78
	79	module_init(dm_zero_init)
	80	module_exit(dm_zero_exit)
	81
bf14299f	82	MODULE_AUTHOR("Jana Saout <[email protected]>");
1da177e4 LT	83	MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
1da177e4 LT	84	MODULE_LICENSE("GPL");